Chapter 10Evolution of Communication

1st lecture

Some functions of communication

Group spacing and coordinationSpecies recognition

Kin recognitionReproduction

Agonism and social statusAlarm

Giving and soliciting of foodSoliciting play

Synchronization of hatching

What is communication?

“Action on the part of one organism (or cell) that alters the pattern ofbehavior in another organism (or cell) in a fashion that is adaptive

to either one or both participants” (E.O. Wilson, 1975)Problem with this definition

If a mouse rustled in the grass, and thereby enabledan owl to catch it, this would be considered communication

“The transmission of a signal for one animal to another such that thesender benefits, on average, from the response of the recipient”

(Slater, 1983)

What does this latter definition assume?

What types of communication signals do animals use?

Some signals are discrete (e.g., ear position),

whereas others are graded (e.g., degree to which mouth

is opened)

Further, note that the meaning of a signal (e.g., opening of

mouth) can vary depending on the context in which it is

displayed

Any given communication signalcan serve multiple functions

e.g., a lion’s roar can function as a spacing device forneighboring prides, as an aggressive display in fightsbetween males, or as a means of maintaining contact

among pride members

Some communication signals even appear to change the meaningof those that follow (i.e., function as metacommunication)

Dogexhibitingplay-bow

Darwin developed the principle of antithesis to help explain the diversityof communication signals within a species

threatening posture

submissive posture

Note that the postural features of these two signals are diametrically opposed to one another (e.g., ear and tail positions, shape of the spine, and piloerection)

This has the effect of accentuating the differences between each signal

Feature of channel

chemical

auditory

visual

tactile Range

long

long

medium

short

Transmission rate

slow

fast

fast

fast

Night-use?

yes

yes

no

yes

Ability to go past objects

good

good

poor

poor

Fade-out time

slow

fast

fast

fast

Locatability

variable

medium

high

high

Energetic cost

low

high

low

low

Type of signal

Each channel of communication has different features

Knowing these features, and a species’ life history, one can make specific predictions about the communication signals on which a species should rely most heavily

e.g., wolves, moths, fish in deep sea vents, howler monkeys

Some signals are “honest” (i.e., convey accurate infromation), whereas others are “deceitful” (i.e., convey

inaccurate information)

Male Australian antlered flies possess bizarre “antlers” that are

thought to serve as a signal to other males, indicating their size

The antlers are said to be an “honest” signal because they accurately reflect each male’s size, and hence potential fighting ability

female 2 males

The functional significance of this signal is that it enables a male to avoid a fruitless and potentially dangerous fight with a larger male

During the breeding season, red deer (elk) stags engage in male-male competition. Instead of initiating potentially dangerous fights, they stand off at a considerable distance from one another and roar at each other.

This is thought to be an “honest” signal because the roaring is a physically demanding activity.

Only the most healthy and fit stags can roar for hours on end.

In most cases, females mate with those males that win the roaring contests

Female fireflies are the femme fatale of the animal

world. They use their abdominal flasher to attract

conspecific males for mating and heterospecific males for

nourishment.

A “deceitful” signaler

Unmated% of responses

Mated% of responses

Femme fatale eating heterospecific male

Unmated females responded most often to conspecific males, whereas mated females responded most often to heterospecific males

Courtship calls are often essential for attracting potential mates

Male Tungara frogs make this “chuck”call continuously over many hours to attract females

Some bats specialize on malefrogs during the mating season,

using their mating calls to locate them

This calling behavior, however, may be exploited by “illegitimate

receivers”

Vervet monkeys emit distinct alarm calls in response to the detection of 3 different types of predators

Notice that the othermonkeys in the troop respond to each alarm call in distinct ways

Two contrasting explanations of the Vervet monkey alarm calls

Meaning hypothesisMonkey produces asemantic signal for

leopardThe leopard call “stands for” or “conjures up imagesof” a leopard even before the monkey has seen the predator, and elicits an adaptive escape response

Acoustical propertyhypothesis

Monkey exhibited its loudest and longest alarm call because the threat posed by the leopard was so

great

The 3 different alarm call types reflect differing degrees of fear or excitement--that elicited by a leopard was the most intense and thus elicited the most dramatic response

How can we determine whether the monkeys areresponding to the acoustical properties or the meaning

of each alarm call?

Approach 1Vary the caller’s apparent level of excitement during a particular

call by altering tape recordings of the call (e.g., make the snake calllonger or shorter, louder or softer). Then observe the responses

of monkeys to these recordings.

Human example would be to pronounce “physical therapy” with two dialects: midwest vs. southern

When Cheyney and Seyfarth ran the experiment, they found that response of the monkeys to different pronunciations of the same

call did not change

What results would you predict based on the acoustical property hypothesis? The meaning hypothesis?

The Chutter call is produced when an

encounter between vervet troops has

escalated into aggressive threats

The Wrr call is produced when an individual vervet spots an approaching troop of vervets

Approach 2In the English language, “treachery” and “deceit” have same meaning

but different acoustical properties; in contrast, “treachery” and “leachery”have similar acoustical properties, but different meaning.

Cheyney and Seyfarth found an analogue to “treachery” and “deceit’ inthe vervet alarm call vocabulary:

Prediction: if these alarm calls have similar meaning to the vervets, then habituation to the Wrr call should generalize to the Chutter call

Note: this test employs a habituation-generalization paradigm

Habituation to the Wrr call generalized to the Chutter call,suggesting that both calls have the same meaning for vervets

In this case, the investigators recorded the amount of time individual

monkeys attended to each call